Q. Hi Kieran
We are buying a new house which is coming with air to water and mechanical ventilation. Do we really need solar PV too?
Thanks
Paula
Cork
A. Hi Paula
Thanks for this question. Great to see that you have managed to get on the property ladder in Ireland. No mean feat these days and it must be daunting when you look at the price you have had to pay and the mortgage (which literally means ‘dead pledge’ in old French!) you have signed up to. It may look like the payments will never end, so rightly you wonder do you really need to fork out even more for solar panels? Let’s see.
So, your new home has both an air to water heat pump and mechanical ventilation. Essentially how this works is you have bought a house with a very efficient eternal envelope which is highly insulated and reasonably airtight. This means that it can maintain a comfortable internal temperature with a small input of heat. In your case this small input of heat comes from a very efficient source, your air to water system. The fact that your house is quite airtight means that you need some form of mechanical ventilation to keep fresh air moving in your house. (older houses don’t have airtightness and therefore don’t really need mechanical ventilation but they are inherently drafty and therefore leak heat in winter). The downside here is that both air to water heating and mechanical ventilation themselves need electrical energy to operate.
Air to water heat pumps essentially remove heat for the air outside and this heat is increased by compression of refrigerant in the heat pump and then transferred to your radiators or underfloor heating in your home. Your mechanical ventilation is an extract pump that removes stale moist air from your house and replaces this with fresh air. Both these systems run hand in hand and help with the efficient movement of warm fresh throughout your house, particularly in the colder months. As such these two systems along with your insulation, airtightness and removal of cold bridging (cold uninsulated spots) will likely provide for an A rating (assuming you have fitted A-Rated windows) but is this enough?
Strictly speaking, yes. You have complied with building regulations so you can sleep well at night knowing you have done your bit for the environment and future generations but there is a potential further opportunity provided by solar photovoltaic panels.
I remember when the war in Ukraine started. We had already suffered from a year of building material inflation the year before and we had hoped it had levelled off and the worst was behind us only to fall victim to fuel inflation associated with this new war in Europe. Essentially fuel that had traditionally been flowing from Russia to Europe was now in jeopardy and most of it was cut off or diverted, This supply shock caused huge spikes in energy costs resulting in electricity prices souring. An unexpected outcome of the beginning of the war was a surge in people looking to install solar panels to offset peak electricity prices. The war has made us much more energy conscious.
When you consider, in tandem, that most new A-rated homes or indeed deep retrofitted older homes now use electricity as their prime energy source, the debate for fitting solar photovoltaic panels to generate your own electricity for free in the sunnier months becomes a real and practical solution.
Though you can generate some electricity in winter, the sun’s energy isn’t as powerful, the daylight hours are shorter, and the weather isn’t generally as favorable. You generate most elasticity in early summer (May is the best month typically) along with good yields in spring in autumn as well. Though your electrical demand will be highest in winter, the savings you make in sunnier months will help offset your electrical bills on an annual basis. During the summer you will often be selling electricity back to your energy supplier which will show as a generation credit on your bill (yes, credit is not a misprint!). You also have the opportunity to store excess electricity in a battery if you fit one to supplement your usage in peak times when your usage exceeds what you are generating. You can also fit an eddi system which allows you to preheat your hot water storage tank with excess electricity. All in all it’s a big upfront investment but here is a great thrill in looking at your savings on the app provided, on a fine day and your (annual) electricity bills.
Kieran McCarthy is a building engineer and director of KMC Homes A-Rated luxury new home builder, serving Cork and Limerick. He is also presenter of a new RTE tv show showcasing deep retrofits in Irish homes due out later this year.
Check out KMC Homes’ brand new website kmchomes.ie
Follow Kieran on instagram @kierankmc for more home building information, tips and Q&A advice.
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